Progesterone-induced protein secretions may serve as a histotrophic nutrient source and provide regulatory functions in blastocyst development. We propose to continue efforts to purify some of the presently uncharacterized proteins in uterine secretions. One approach will be to generate monoclonal antibodies by the hybridoma technology and use these to purify specific proteins by affinity chromatography. The regulatory effects of sex steroids on proteins that may transport vitamins D3 and riboflavin and minerals such as calcium will be evaluated. The presence of protease inhibitor in uterine secretions will be studied with respect to possible regulatory effects of these proteins on blastocyst development. Two major polypeptides identifed in sheep uterine secretions will be studied with respect to their site of synthesis, movement and possible function. The relationship between hormonal status, rate of protein secretion and levels of translatable mRNA will be assessed in an attempt to understand better how the synthesis of uterine proteins is regulated. A major effort will be directed toward developing an understanding of how the purple glycoprotein, uteroferrin (Uf), from the pig transports iron. We will attempt to learn: (1) How Uf is transported; (2) whether there are Uf receptors on the trophoblast; (3) how iron is unloaded and, (4) how estrogen modulates Uf secretion. These experiments should allow us to gain a better understanding of the role of progesterone-induced protein secretions in the pregnant uterus and how they may affect fertility.